Railroad rails that are used for heavy load railroads and curved sections are required to have more abrasion resistance than ordinary rails. For this reason, after undergoing hot rolling, during the time from the austenite region temperature until the end of the pearlite transformation, a process is performed to raise the strength of the rail head portion by accelerated cooling. In recent years, in order to further improve the abrasion resistance, a pearlitic rail has been developed and put to practical use in which the carbon content is increased until the hypereutectoid region (Refer to Patent Document 1).
However, when the carbon content is increased in order to improve abrasion resistance, problems such as proeutectoid cementite readily forming in the rail head portion, and the toughness and ductility of the rail dropping sharply occur.
Therefore, Patent Document 2 discloses a pearlite rail manufacturing method in which, in order to suppress the formation of proeutectoid cementite in the pillar portion of a rail, and stably generate a pearlite microstructure with a high degree of hardness and a high cementite ratio in the railhead, a railhead is subjected to accelerated cooling from the austenitic region temperature to 700 to 500° C. at a rate of 1 to 10° C./second, and moreover the pillar of this rail is subjected to accelerated cooling from the austenitic region temperature to 750 to 600° C. at a rate of 1 to 10° C./second.
In addition, as accelerated cooling methods for a rail employing different cooling mediums, there are (1) methods that use a mist (Patent Documents 3 to 5), methods that use a gas such as air (Patent Documents 6 and 7) and methods that immerse the railhead in a cooling liquid (Patent Documents 8 and 9).
[Patent Document 1] Japanese Unexamined Patent Application, First publication No. H08-144016
[Patent Document 2] Japanese Unexamined Patent Application, First publication No. H09-137228
[Patent Document 3] Japanese Unexamined Patent Application, First publication No. S47-7606
[Patent Document 4] Japanese Unexamined Patent Application, First publication No. S54-147124
[Patent Document 5] Japanese Unexamined Patent Application, First publication No. H08-319515
[Patent Document 6] Japanese Unexamined Patent Application, First publication No. S61-149436
[Patent Document 7] Japanese Unexamined Patent Application, First publication No. S61-279626
[Patent Document 8] Japanese Unexamined Patent Application, First publication No. S57-85929
[Patent Document 9] Japanese Unexamined Patent Application, First publication No. H08-170120